In general, when an engine output torque is excessive the vehicle tends to make a sudden shift, and the driving wheels may skid.
To cope with such inconveniences, some modern motor vehicles are equipped with a running state control system which decreases the engine output torque based on intake air amount control by tandem throttle valves, by ignition retardation control, by fuel supply cutoff control and the like when the engine is in an overload state. See JP-A 62-31769, for example.
With known running state control systems for a motor vehicle, however, if tandem throttle valves are used for controlling the engine output torque, the throttle chamber becomes very different in structure from the conventional one, resulting in a great increase in the manufacturing cost.
On the other hand, if ignition retardation control or fuel supply cutoff control is adopted to regulate the engine output torque, the resulting unstable engine combustion adversely affects the catalyzer arranged in the exhaust system.